Hunger and thirst

Ghrelin

(hunger) a hormone that is produced and released mainly by the stomach with small amounts also being released by the small intestine, pancreas and brain. Ghrelin stimulates appetite, increases food intake and promotes fat storage. When administered to humans, ghrelin increases food intake by up to 30% by circulating in the bloodstream at the hypothalamus, an area of the brain crucial in the control of appetite. Ghrelin levels are primarily regulated by food intake. Levels of Ghrelin in the blood rise just before eating and when fasting, with the timing of these rises being affected by our normal meal routine. Levels of ghrelin increase when fasting and are lower in individuals with a higher body weight compared to lean individuals

Insulin

(satiety than high) enables glucose to enter cells. When insulin levels are high, cells receive glucose easily. When someone is getting ready for a meal. insulin levels rise, letting some of the blood glucose enter the cells in preparation for the ruch of additional glucose about to enter the blood. Insulin increases even more during and after a meal. Higher levels of insulin decrease appetite

CCK

(satiety) food in the duodenum releases this hormone which limits meal sizes in 2 ways 1. CCK closes the squinter muscle between the stomach and the duodenum causing the stomach to hold its contents and fill more quickly than usual 2. CCK stimulates the vague nerve, which sends a message to the hypothalamus, causing cells there to release a neurotransmitter that is a shorter version of the CCK molecule itself

PYY

(satiety) secreted into the circulation by cells of the small and large instetsine, the small peptide pyy3-36 is at a low level in the blood prior to eating, but that level rises rapidly on ingestion of a meal

Leptin

(satiety) signals the brain about body's fat reserves, providing a long-term indicator of wether meals have been too large or too small. Each meal also increases the release of leptin, so the amount of circulating leptin indicates something about short-term nutrition as well

Osmotic thirst

Eating salty foods causes osmotic thirst. The solutes inside and outside a cell produce an osmotic pressure, the tendency of water to flow across a semipermaeble membrane from the area of low solute concentration to the area of higher concentration. A semipermaeble membrane is one through which water can pass but solute cannot. Osmotic pressure occurs when solutes are more concentrated on one side of the membrane than on the other. The brain gets information from receptors in the stomach that detects high levels of sodium, enabling the brain to anticipate an osmotic need before the rest of the body actually experience it

Lipostatic theory

Every person has a set point for body weight. Abnormalities of this set point creates changes in eating behavior, so that the body's fat will come back to the set point

Metabolic phases

Most cells regulate the import of glucose molecules via glucose transporters that span cell membrane and bring glucose molecules from outside the cell into the cell for use. Most of your body requires unsulin to make use of that glucose. It is used in three mechanisms: 1. CEPHALIC PHASE - sensory stimuli from food (sight, smell, taste) evoke release of insulin in anticipation of glucose arrival in blood 2. DIGESTIVE PHASE - food entering the stomach and intestines causes them to release gut hormones, some of which stimulate the pancreas to release insulin 3. ABSORPTIVE PHASE - special cells in the liver (gluco-detector) detect glucose entering the bloodstream and signal the pancreas to release insulin 4. FASTING PHASE: the point in which the unstored energy is used snd the body has to use the stored energy

Positive-incentive theory (also with drugs)

People and animals aren't motivated to eat due to internal energy deficienty, but do to the pleasure of eating. Eating is also controlled like sexual behavior. The presence of food is important

Ventromedial Hypothalamus (VMH)

Satiety, damage in this area causes overeating. It has 2 phases: Dynamic (gaining weight, overeating) and static (stable overweight). It increases insulin levels which causes lipogenesis; production of body fat

Osmosensory neuron

Specialized neuron that measures the movement of water in and out of the intracellular side. These neurons have no constant volume. They also have channels that open and close when the cell membrane changes. Molecules have the tendency to spread, so they go from high conentration to low concentration. The power that pulls water through the membrane is called osmotic pressure. The concentration of a solute is called osmolality

Signals that start and stop hunger

The most immediate source of energy for the body is the collection of complex carbohydrates in our diet that are rapidly broken down into simple sugars that cells can use GLUCOSE - is an important sugar molecule used by the body and brain for energy GLYCOGEN - converted by glucose, it is used to store short terme energy LIPIDS - used for longterm storage of energy

Hypovolumic thirst

Thirst based on loss of volume, such as excessive loss of fluids like blood (menstruation), sweating and diarrhea. When blood volume drops, the kidney release the enzyme rennin, which splits a portion of angiotensinogen, a large protein in the blood, to form ANGIOTENSIN I constricts the blood vessels compensating for the drop in blood pressure. Angiotensin II also helps trigger thirst in conjunction with receptors that detect blood pressure in the large veins. You need to restore lost salts and not just water

boulimia

also called bulimia nervosa. A syndrome in which individuals periodically gorge themselves, usually with junk food, and then either vomit or take laxatives to avoid weight gain

Allostasis

body maitains a higher temperature during the day than at night, even if room teperature is the same. It has dynamic changes in stpoints

Vague nerve

conveys information about the stretching of the stomach walls, providing a major basis for satiety

Satiety

full feeling which makes you stop eating. Food in the intestines and glucose of the blood stimulate satiety levels. These signals depend on the volume and the nutritive density of the food. The amount we eat is influenced by previous experiences and the psychological effect of that specific meal

Shamfeeding

intake of food by an animal with a surgically created esophageal fistula that prevents the ingested food from reaching the stomach. Used in studies of physiological and psychological mechanisms of hunger and feeding behavior

Set-point assumption

most people assume that hunger comes due to a lack of energy. Eating is used to make the energy sources in the body optimal. After a meal, an energy source will come close to the set point. All set point systems are negative feedback systems

Lateral hypothalamus (LH)

output from the paraventricular nucleus acts on the lateral hypothalamus, which includes so many neurons and passing axons that it has been compared to a crowded train station. The ateral hypothalamus controls insulin secretion, alters taste responsiveness, and faciliates feeding in other ways. Damage in this area causes aphagia, where someone refuses food and water

Negative feedback

processes that reduce inconsistency from the set point. Much of motivated behavior can be described as negative feedback: something happens to cause a disturbance and behavior varies until it relieves the disturbance

Appetizer effect

small amounts of food before a meal increase hunger. The amount of consumtion depends on the served size. The bigger it is, the more we wnat to eat. We eat also more when we are among others

Glucagon

stimulates the liver to convert some of its stored glycogen to glucose to replenish low supplies in the blood

Homeostasis

temperature regulation and other biological processes that keep our body variable within a fixed range. It triggers physiological and behavioral activities that keep our body variable within a fixed range. It triggers physiological and behavioral activities that keep certain variables within a set range. In many cases, the range is so narrow that we refer it as a setpoint, a single value that the body works to maintain

Settling Point

the body's weight has a tendency to vary at a certain point; the level where many factors influence body weight to reach an equilibrium

Premeal hunger

the energy reserves are balanced homeostatically right before a meal. This balance becomes irregular as soon as someone eats. The bod ytries to prevent this by going through a cephalic phase right before a meal

Glucostatic theory

when the glucose level goes below a certain level (set point), we become hungry. Eating makes sure that the level will come abck to the set point

Hypovolemic shock

when you loose 1/5 of blood